The invention relates to substituted pyrrole compounds which are useful as kinase inhibitors, more specifically useful as checkpoint kinase 1 (chk1) inhibitors, thus useful as cancer therapeutics. The invention also relates to compositions, more specifically pharmaceutical compositions comprising these compounds and methods of using the same to treat various forms of cancer and hyperproliferative disorders, as well as methods of using the compounds for in vitro, in situ, and in vivo diagnosis or treatment of mammalian cells, or associated pathological conditions.
Individual cells replicate by making an exact copy of their chromosomes, and then segregating these into separate cells. This cycle of DNA replication, chromosome separation and division is regulated by mechanisms within the cell that maintain the order of the steps and ensure that each step is precisely carried out. Involved in these processes are the cell cycle checkpoints (Hartwell et al., Science, Nov. 3, 1989, 246(4930):629-34) where cells may arrest to ensure DNA repair mechanisms have time to operate prior to continuing through the cycle into mitosis. There are two such checkpoints in the cell cycle—the G1/S checkpoint that is regulated by p53 and the G2/M checkpoint that is monitored by the serine/threonine kinase checkpoint kinase 1 (chk1).
Chk1 and Chk2 are structurally unrelated yet functionally overlapping serine/threonine kinases activated in response to genotoxic stimuli (reviewed in Bartek et al., Nat. Rev. Mol. Cell Biol. 2001, vol. 2, pp. 877-886). Chk1 and Chk2 relay the checkpoint signals from the ATM and ATR, which phosphorylate and activate them. Chk2 is a stable protein expressed throughout the cell cycle, activated mainly by ATM in response to double-strand DNA breaks (DSBs). In contrast, Chk1 protein expression is largely restricted to S and G2 phases. In response to DNA damage, ChK1 is phosphorylated and activated by ATM/ATR, resulting in cell cycle arrest in the S and G2/M phases to allow for repair of DNA damage (reviewed in Cancer Cell, Bartek and Lukas, Volume 3, Issue 5, May 2003, Pages 421-429. Inhibition of Chk1 has been shown to abrogate cell cycle arrest leading to enhanced tumor cell death following DNA damage by a range of chemotherapeutics. Cells lacking intact G1 checkpoints are particularly dependent on S and G2/M checkpoints and are therefore expected to be more sensitive to chemotherapeutic treatment in the presence of a chk1 inhibitor, whereas normal cells with functional G1 checkpoints would be predicted to undergo less cell death.